1. Field of the Invention
This Invention relates to a color converting system for detecting a specified color and converting the specified color into another specific color in an image processing equipment, such as copying machines, printers, and facsimile machines, for reproducing images recorded on an original sheet.
2. Description of the Related Art
A color image processing equipment, such as copying machines, read a color original sheet by means of a CCD line sensor to produce anaslog color decomposing signals and then, after converting the analog signals into digital signals, perform various processing operations. For example, since the color decomposing signals as read by means of the CCD line sensor are the signals obtained through detection of the light reflected from the original sheet, reproduction of the original on copying paper is performed by converting the color decomposing signals into recording signals for coloring materials (colorants), such as toners, forming a latent image on a photosensitive material by irradiating it with a laser beam modulated in accordance with the recording signals, material, and then developing, transferring, and fusing the images. In general practice, editing processes are performed in stages before the recording signals in the form of gradation signals are converted into on-off signals for the laser beam.
In the above digital image processing equipment, such as copying machines, printers, and facsimile machines, which is capable of reproducing an original sheet by processing it with digital signals, it is possible to set an area arbitrarily and to perform various types of editing processes, including color conversion, by performing operations of replacement, movement, etc. on the digital signals in such an area. In a color image processing equipment, for example, it is possible to perform color conversion by replacing the input image data with specific image data as specified for a particular area. By virtue of this feature, conversion into a monochromatic image, a black-and-white image or an image in a particular color can be performed in a specified area.
In order to perform the conversion of a particular color to be replaced (a comparison color) into a particular replacing color, it is necessary to specify both the color to be replaced and the replacing color. Japanese Patent Application Unexamined Publication No. 46380-1987 discloses a method of specification of color for such color conversion in a color printing/displaying equipment. The code data containing color specifying information sent out of a host system are temporarily stored in a source buffer memory, and the code data are then converted into bit data and stored in a bit map memory prepared for individual color types, i.e., N colors. This color printing/displaying equipment is also provided with an extracting color register which is used for specifying a color to be replaced, and a replacing color register which stores the data on the replacing color. In case it is found by comparison that the output from the bit map memory and the specified color in the extracting color register are in agreement, the equipment gives priority to and outputs, at the time of the agreement, the data in the replacing color register instead of the output from the bit map memory.
Moreover, as other examples of the editing processes, there is a process in which in case binary images such as characters and line drawings, and halftone images such as photographs and printed materials in halftone mesh are present in mixture, the resolution, grain properties and the reproducibility of chromatic gradation is improved in accordance with each image through application of an edge emphasizing process to the binary image with a change in a filter coefficient and a smoothing process to the halftone image, or by changing a threshold matrix of a screen generator. There also performed are color balance control and tone control such as contrast adjustment and density control.
However, it is extremely difficult for an operator to specify the color with accuracy. Even in the case of the specification of the primary colors, which is considered the simplest task, it frequently happens that the color area which is judged as the same color from the human perception is different from the area judged as the same color in terms of the color components. Accordingly, in an attempt of detecting a particular color and performing a color converting operation on the detected color, there sometimes occurs the problem that the color which should be detected from the human perception is not detected, so that a dispersion occurs in the color conversion process. In specific terms, the detection of the color blue, for example, is liable in some cases to a failure that the colors which appear to be blue in the visual perception are not detected as blue because the individual decomposed colors present subtle differences. On the contrary, the colors which are judged to be different in visual perception may in some cases are judged to be identical, so that those colors are detected at the same time, giving rise to the problem that the intended color conversion cannot be accomplished.
Furthermore, since the color conversion can be performed in a plurality of specified areas, it will be extremely difficult for an operator to perform the editing work while taking account of overlapping of the areas and the color conversion at the same time. Thus, it will be a subject in the color conversion performed together with the specification of areas to find out how to deal with the contention of colors in one area and the overlapping of areas.
A special case to be taken into consideration in connection with the color conversion in a specified area is the so-called marker editing process. By the term, marker, is meant a pen or the like which is used to indicate a special relation between the information on the original sheet and the color of the marker and the area by applying to the original sheet an overlay of a color in such density as permits the recognition of the characters on the original sheet. The marker editing process means the process of reading the information on the marker color and the marked area as indicated on the original sheet with a marker and utilizing such information for the editing work such as color conversion.
However, the marker editing process is affected considerably by such factors as the color distribution of the marker, the type of the marker, the degree of its deterioration, the intensity of marking, and the quality of paper. For instance, markers offered by different manufacturers are different in their color distribution, and there are varions types, such as a fluorescent ink type and a paint type. Moreover, even the same marker will produce different shades of color in visual perception depending on the quality of paper of such varieties as PPC paper, coating paper and the ordinary paper. Furthermore, the marking density will vary, depending on the density (degree of deterioration) of the marker and the number of times of repeated marking. Consequently, it is not possible to specify in a simple manner the threshold value for the recognition of the marker, and this causes the problem that the system is liable to the occurrence of editing errors due to a failure to recognize a marking and the occurrence of copying defects due to the wrong recognition of a marking.
FIG. 52 presents examples of color distribution of marking by markers of various densities on the various types of paper, i.e., PPC paper, coating paper and the ordinary paper. FIG. 52(a) shows the ranges of Y, M and C in 256 chromatic gradations marked with the marker manufactured by Company A (a non-transparent blue marker) while FIG. 52(b) shows the Y, M and C ranges in 256 chromatic gradations marked with the marker manufactured by Company B (a semi-transparent blue marker).
For example, the range for Y (low density) on the coating paper is from 34 to 48 in FIG. 52(a), but the range for Y (low density) on the same coating paper is from 6 to 12 in FIG. 52(b). Similarly, the range for C (low density) on the coating paper is from 40 to 78 in FIG. 52(b) while the range of C (high density) on the PPC paper is from 116 to 158 in the same figure, thus presenting a wide range of dispersion. Therefore, if the threshold values are to be set in such a way as to include all these values in the range of recognition, the threshold value for Y will be in the range from 0 to 54, that for M will be in the range from 0 to 50, and that for C will be in the range from 40 to 255. However, these three ranges of threshold value commonly include the range from 40 to 50, with a result that gray (highlight gray) will be recognized in this range. In other words, the part in highlight gray in halftone images on an original sheet in black and white will be recognized erroneously as the color of the marker. As a result, mistakes in the pickup and drop of the marker will take place, so that defects in the highlight part will eventually be conspicuous. That is, some image data is erroneously recognized as a marker and recognition of the marker is failed. Consequently, there occurs the problem that the highlight part in the image data is deleted as a result of the erroneous recognition of that part as a marker, or an area other than the area for editing is subjected to an editing operation. On one hand, part of the marking is output (recorded), without being deleted. The upper-limit portions of Y and M, as well as the lower-limit portion of C may be compressed in order to eliminate the erroneous recognition of this highlight gray, but then there arises another problem of the pickup error in which a marker with a thinned edge area, for example, fails to be recognized and is eventually recorded in the course of the main scanning process.